Because of its excellent rigidity, heat resistance and impact resistance, polypropylene is molded by various molding processes and used in many fields. The properties required for the polypropylene differ from each other according to the molding process or the use of the polypropylene. For example, when the polypropylene is used as a material of sewage pipe, potable water pipe or gas pipe, excellent pipe fatigue properties, mechanical strength and moldability are required for the polypropylene. Recently, there has been a growing demand for improvement in rigidity for the purpose of increasing economical efficiency by for example thinning the pipe wall, and there has been a growing demand for improvement in moldability for the purpose of decreasing electric power consumption. When the polypropylene is used as a material of films, impact resistance is required and also transparency is occasionally required for the polypropylene.
The present inventors have studied propylene polymer compositions capable of producing heat molded products, particularly pipes and films, having excellent mechanical strength, and as a result they have found that heat molded products having excellent mechanical strength can be obtained from a composition comprising a propylene polymer of lower density which has a specific melt flow rate and a specific temperature at the maximum peak position of an endothermic curve measured by a differential scanning calorimeter and a propylene polymer of higher density which has a specific melt flow rate and a specific temperature at the maximum peak position of an endothermic curve measured by a differential scanning calorimeter and that pipes and films obtained from the composition particularly have excellent properties. Based on the finding, the present invention has been accomplished.